This chapter is about 70% Commodus and 30% Pertinax; the former reigned for 13 years and the latter less than three months. Though from what Gibbon says, Pertinax is much the more attractive of the two as characters. A lot about Commodus himself, but it is rather long on outrage at his infamy (...infamy, they've all got it in for me) and short on detail; compared to Caligula he seems fairly small beer.
But then the story of Pertinax is told succinctly and well, actually rather moving in places - an old man, unexpectedly made emperor, trying to do his best to undo his predecessor's mistakes and then move forward, but who is then very quickly brought down by the military. If you don't know what's coming (and I didn't) the end of the chapter is a brutal shock.